Systems, articles, and methods for electromyography sensors

ABSTRACT

Systems, articles, and methods for surface electromyography (“EMG”) sensors that combine elements from traditional capacitive and resistive EMG sensors are described. For example, capacitive EMG sensors that are adapted to resistively couple to a user&#39;s skin are described. Resistive coupling between a sensor electrode and the user&#39;s skin is galvanically isolated from the sensor circuitry by a discrete component capacitor included downstream from the sensor electrode. The combination of a resistively coupled electrode and a discrete component capacitor provides the respective benefits of traditional resistive and capacitive (respectively) EMG sensor designs while mitigating respective drawbacks of each approach. A wearable EMG device that provides a component of a human-electronics interface and incorporates such capacitive EMG sensors is also described.

BACKGROUND Technical Field

The present systems, articles, and methods generally relate toelectromyography and particularly relate to capacitive electromyographysensors that resistively couple to the user's body.

Description of the Related Art Wearable Electronic Devices

Electronic devices are commonplace throughout most of the world today.Advancements in integrated circuit technology have enabled thedevelopment of electronic devices that are sufficiently small andlightweight to be carried by the user. Such “portable” electronicdevices may include on-board power supplies (such as batteries or otherpower storage systems) and may be designed to operate without anywire-connections to other electronic systems; however, a small andlightweight electronic device may still be considered portable even ifit includes a wire-connection to another electronic system. For example,a microphone may be considered a portable electronic device whether itis operated wirelessly or through a wire-connection.

The convenience afforded by the portability of electronic devices hasfostered a huge industry. Smartphones, audio players, laptop computers,tablet computers, and ebook readers are all examples of portableelectronic devices. However, the convenience of being able to carry aportable electronic device has also introduced the inconvenience ofhaving one's hand(s) encumbered by the device itself. This problem isaddressed by making an electronic device not only portable, butwearable.

A wearable electronic device is any portable electronic device that auser can carry without physically grasping, clutching, or otherwiseholding onto the device with their hands. For example, a wearableelectronic device may be attached or coupled to the user by a strap orstraps, a band or bands, a clip or clips, an adhesive, a pin and clasp,an article of clothing, tension or elastic support, an interference fit,an ergonomic form, etc. Examples of wearable electronic devices includedigital wristwatches, electronic armbands, electronic rings, electronicankle-bracelets or “anklets,” head-mounted electronic display units,hearing aids, and so on.

Human-Electronics Interfaces

A wearable electronic device may provide direct functionality for a user(such as audio playback, data display, computing functions, etc.) or itmay provide electronics to interact with, communicate with, or controlanother electronic device. For example, a wearable electronic device mayinclude sensors that are responsive to (i.e., detect and provide one ormore signal(s) in response to detecting) inputs effected by a user andtransmit signals to another electronic device based on those inputs.Sensor-types and input-types may each take on a variety of forms,including but not limited to: tactile sensors (e.g., buttons, switches,touchpads, or keys) providing manual control, acoustic sensors providingvoice-control, electromyography sensors providing gesture control, oraccelerometers providing gesture control.

A human-computer interface (“HCI”) is an example of a human-electronicsinterface. The present systems, articles, and methods may be applied toHCIs, but may also be applied to any other form of human-electronicsinterface.

Electromyography Sensors

Electromyography (“EMG”) is a process for detecting and processing theelectrical signals generated by muscle activity. EMG devices employ EMGsensors that are responsive to the range of electrical potentials(typically μV-mV) involved in muscle activity. EMG signals may be usedin a wide variety of applications, including: medical monitoring anddiagnosis, muscle rehabilitation, exercise and training, prostheticcontrol, and even in controlling functions of electronic devices (i.e.,in human-electronics interfaces).

There are two main types of EMG sensors: intramuscular EMG sensors andsurface EMG sensors. As the names suggest, intramuscular EMG sensors aredesigned to penetrate the skin and measure EMG signals from within themuscle tissue, while surface EMG sensors are designed to rest on anexposed surface of the skin and measure EMG signals from there.Intramuscular EMG sensor measurements can be much more precise thansurface EMG sensor measurements; however, intramuscular EMG sensors mustbe applied by a trained professional, are obviously more invasive, andare less desirable from the patient's point of view. The use ofintramuscular EMG sensors is generally limited to clinical settings.

Surface EMG sensors can be applied with ease, are much more comfortablefor the patient/user, and are therefore more appropriate fornon-clinical settings and uses. For example, human-electronicsinterfaces that employ EMG, such as those proposed in U.S. Pat No.6,244,873 and U.S. Pat. No. 8,170,656, usually employ surface EMGsensors. Surface EMG sensors are available in two forms: resistive EMGsensors and capacitive EMG sensors. The electrode of a resistive EMGsensor is typically directly electrically coupled to the user's skinwhile the electrode of a capacitive EMG sensor is typically capacitivelycoupled to the user's skin. That is, for a resistive EMG sensor, theelectrode typically comprises a plate of electrically conductivematerial that is in direct physical contact with the user's skin, whilefor a capacitive EMG sensor, the electrode typically comprises a plateof electrically conductive material that is electrically insulated fromthe user's skin by at least one thin intervening layer of dielectricmaterial or cloth.

Resistive EMG sensors and capacitive EMG sensors both have relativeadvantages and disadvantages. For example, the resistive coupling to theskin realized by a resistive EMG sensor provides a relatively lowimpedance (compared to a capacitive coupling) between the skin and thesensor and this can greatly simplify the circuitry needed to amplify thedetected EMG signals; however, because this resistive coupling isessentially galvanic and uninterrupted, it can also undesirably coupleDC voltage to the amplification circuitry and/or result in a voltageapplied to the skin of the user. Both of these effects potentiallyimpact the quality of the EMG signals detected. On the other hand, thecapacitive coupling to the skin realized by a capacitive EMG sensorgalvanically isolates the amplification circuitry from the skin andthereby prevents a DC voltage from coupling to the amplificationcircuitry and prevents a voltage from being applied to the skin;

however, this capacitive coupling provides a relatively high impedancebetween the skin and the sensor and this can complicate the circuitryneeded to amplify the detected EMG signals (thus making theamplification circuitry more expensive). The strength of the capacitivecoupling can also vary widely from user to user. Clearly, neither typeof surface EMG sensor is ideal and there is a need in the art forimproved surface EMG sensor designs.

BRIEF SUMMARY

An electromyography (“EMG”) sensor may be summarized as including afirst sensor electrode formed of an electrically conductive material; anamplifier; a first electrically conductive pathway that communicativelycouples the first sensor electrode and the amplifier; a first capacitorelectrically coupled in series between the first sensor electrode andthe amplifier in the first electrically conductive pathway; and a firstresistor electrically coupled in series between the first sensorelectrode and the amplifier in the first electrically conductivepathway. The first capacitor and the first resistor may be electricallycoupled in series with one another in the first electrically conductivepathway. The EMG sensor may further include: a second electricallyconductive pathway that communicatively couples to ground; a thirdelectrically conductive pathway that communicatively couples the firstelectrically conductive pathway and the second electrically conductivepathway; a second capacitor electrically coupled in the thirdelectrically conductive pathway in between the first electricallyconductive pathway and the second electrically conductive pathway; afourth electrically conductive pathway that communicatively couples thefirst electrically conductive pathway and the second electricallyconductive pathway; and a second resistor electrically coupled in thefourth electrically conductive pathway in between the first electricallyconductive pathway and the second electrically conductive pathway. TheEMG sensor may be a differential EMG sensor that further includes: asecond sensor electrode formed of an electrically conductive material; afifth electrically conductive pathway that communicatively couples thesecond sensor electrode and the amplifier; a third capacitorelectrically coupled in series between the second sensor electrode andthe amplifier in the fifth electrically conductive pathway; and a thirdresistor electrically coupled in series between the second sensorelectrode and the amplifier in the fifth electrically conductivepathway. The third capacitor and the third resistor may be electricallycoupled in series with one another in the fifth electrically conductivepathway. The EMG sensor may further include: a sixth electricallyconductive pathway that communicatively couples the fifth electricallyconductive pathway and the second electrically conductive pathway; afourth capacitor electrically coupled in the sixth electricallyconductive pathway in between the fifth electrically conductive pathwayand the second electrically conductive pathway; a seventh electricallyconductive pathway that communicatively couples the fifth electricallyconductive pathway and the second electrically conductive pathway; and afourth resistor electrically coupled in the seventh electricallyconductive pathway in between the fifth electrically conductive pathwayand the second electrically conductive pathway. The EMG sensor mayfurther include a ground electrode formed of an electrically conductivematerial and communicatively coupled to the second electricallyconductive pathway.

The first sensor electrode may comprise a first layer formed of a firstelectrically conductive material and a second layer formed of a secondelectrically conductive material. The first electrically conductivematerial may include copper. The second electrically conductive materialmay include at least one material selected from the group consisting of:gold, steel, stainless steel, silver, titanium, electrically conductiverubber, and electrically conductive silicone.

The EMG sensor may further include a housing, wherein the amplifier, thefirst electrically conductive pathway, the first capacitor, the firstresistor, and the first layer of the first sensor electrode are allsubstantially contained within the housing, the housing including ahole, and wherein at least a portion of the second layer of the firstsensor electrode extends out of the housing through the hole. The EMGsensor may further include a substrate having a first surface and asecond surface, the second surface opposite the first surface across athickness of the substrate, wherein the first sensor electrode iscarried by the first surface of the substrate and the amplifier, thefirst capacitor, and the first resistor are all carried by the secondsurface of the substrate. The first electrically conductive pathway mayinclude at least one via that extends through the substrate. The firstelectrically conductive pathway may include at least one electricallyconductive trace carried by the second surface of the substrate. Thefirst capacitor and the first resistor may include respective discreteelectronic components.

A method of fabricating an electromyography (“EMG”) sensor may besummarized as including: forming a first sensor electrode on a firstsurface of a substrate, wherein forming a first sensor electrode on afirst surface of a substrate includes depositing at least a first layerof a first electrically conductive material on the first surface of thesubstrate; depositing an amplifier on a second surface of the substrate,the second surface opposite the first surface across a thickness of thesubstrate; depositing a first capacitor on the second surface of thesubstrate; depositing a first resistor on the second surface of thesubstrate; and forming a first electrically conductive pathway thatcommunicatively couples the first sensor electrode and the amplifierthrough the first capacitor and the first resistor. Forming the firstelectrically conductive pathway may include forming a via through thesubstrate. Depositing at least a first layer of a first electricallyconductive material on the first surface of the substrate may includedepositing a first layer including copper on the first surface of thesubstrate, and forming the first sensor electrode may further includedepositing a second layer of a second electrically conductive materialon the first layer of the first electrically conductive material, thesecond electrically conductive material including a material selectedfrom the group consisting of: gold, steel, stainless steel, silver,titanium, electrically conductive rubber, and electrically conductivesilicone.

The method may further include enclosing the substrate in a housing,wherein the housing includes a hole, and wherein enclosing the substratein a housing includes enclosing the amplifier, the first capacitor, andthe first resistor in the housing and aligning the first sensorelectrode with the hole, wherein at least a portion of the second layerof the second electrically conductive material protrudes out of thehousing through the hole.

The method may further include forming a ground electrode on the firstsurface of the substrate; forming a second electrically conductivepathway that communicatively couples to the ground electrode; depositinga second capacitor on the second surface of the substrate; forming athird electrically conductive pathway that communicatively couples thefirst electrically conductive pathway and the second electricallyconductive pathway through the second capacitor; depositing a secondresistor on the second surface of the substrate; and forming a fourthelectrically conductive pathway that communicatively couples the firstelectrically conductive pathway and the second electrically conductivepathway through the second resistor. The EMG sensor may be adifferential EMG sensor, and the method may further include: forming asecond sensor electrode on the first surface of the substrate;depositing a third capacitor on the second surface of the substrate;depositing a third resistor on the second surface of the substrate; andforming a fifth electrically conductive pathway that communicativelycouples the second sensor electrode and the amplifier through the thirdcapacitor and the third resistor. The method may further include:depositing a fourth capacitor on the second surface of the substrate;forming a sixth electrically conductive pathway that communicativelycouples the fifth electrically conductive pathway and the secondelectrically conductive pathway through the fourth capacitor; depositinga fourth resistor on the second surface of the substrate; and forming aseventh electrically conductive pathway that communicatively couples thefifth electrically conductive pathway and the second electricallyconductive pathway through the fourth resistor.

Depositing the amplifier on the second surface of the substrate mayinclude soldering the amplifier on the second surface of the substrate;depositing the first capacitor on the second surface of the substratemay include soldering the first capacitor on the second surface of thesubstrate; and/or depositing the first resistor on the second surface ofthe substrate may include soldering the first resistor on the secondsurface of the substrate.

A wearable electromyography (“EMG”) device may be summarized asincluding: at least one EMG sensor responsive to (i.e., to detect andprovide at least one signal in response to) muscle activitycorresponding to a gesture performed by a user of the wearable EMGdevice, wherein in response to muscle activity corresponding to agesture performed by a user the at least one EMG sensor providessignals, and wherein the at least one EMG sensor includes: a firstsensor electrode formed of an electrically conductive material; anamplifier; a first electrically conductive pathway that communicativelycouples the first sensor electrode and the amplifier; a first capacitorelectrically coupled in series between the first sensor electrode andthe amplifier in the first electrically conductive pathway; and a firstresistor electrically coupled in series between the first sensorelectrode and the amplifier in the first electrically conductivepathway; a processor communicatively coupled to the at least one EMGsensor to in use process signals provided by the at least one EMGsensor; and an output terminal communicatively coupled to the processorto transmit signals output by the processor. The at least one EMG sensormay further include: a second electrically conductive pathway thatcommunicatively couples to ground; a third electrically conductivepathway that communicatively couples the first electrically conductivepathway and the second electrically conductive pathway; a secondcapacitor electrically coupled in between the first electricallyconductive pathway and the second electrically conductive pathway in thethird electrically conductive pathway; a fourth electrically conductivepathway that communicatively couples the first electrically conductivepathway and the second electrically conductive pathway; and a secondresistor electrically coupled in between the first electricallyconductive pathway and the second electrically conductive pathway in thefourth electrically conductive pathway. The at least one EMG sensor mayinclude at least one differential EMG sensor, and the at least onedifferential EMG sensor may further include: a second sensor electrodeformed of an electrically conductive material; a fifth electricallyconductive pathway that communicatively couples the second sensorelectrode and the amplifier; a third capacitor electrically coupled inbetween the second sensor electrode and the amplifier in the fifthelectrically conductive pathway; and a third resistor electricallycoupled in between the second sensor electrode and the amplifier in thefifth electrically conductive pathway. The at least one EMG sensor mayfurther include a ground electrode formed of an electrically conductivematerial and communicatively coupled to the second electricallyconductive pathway.

The first sensor electrode of the at least one EMG sensor may comprise afirst layer formed of a first electrically conductive material and asecond layer formed of a second electrically conductive material. Thefirst electrically conductive material may include copper. The secondelectrically conductive material may include at least one materialselected from the group consisting of: gold, steel, stainless steel,silver, titanium, electrically conductive rubber, and electricallyconductive silicone. The wearable EMG device may further include: atleast one housing that at least partially contains the at least one EMGsensor, wherein the amplifier, the first electrically conductivepathway, the first capacitor, the first resistor, and the first layer ofthe first sensor electrode are all substantially contained within the atleast one housing, the at least one housing including a hole, andwherein at least a portion of the second layer of the first sensorelectrode extends out of the at least one housing through the hole.

A capacitive electromyography (“EMG”) sensor may be summarized asincluding: a first sensor electrode to in use resistively couple to auser's skin, wherein the first sensor electrode includes a plate ofelectrically conductive material; circuitry communicatively coupled tothe first sensor electrode of the capacitive EMG sensor; and a firstcapacitor to in use galvanically isolate the circuitry from the user'sskin, the first capacitor electrically coupled in series between thefirst sensor electrode and the circuitry. Resistive coupling between thefirst sensor electrode and the user's skin may include an impedance, andthe capacitive EMG sensor may further include a first resistor to in usedominate the impedance of the resistive coupling between the firstsensor electrode and the user's skin, wherein the first resistor iselectrically coupled in series between the first sensor electrode andthe circuitry and wherein the first resistor has a magnitude of at least1 kΩ. The first resistor may have a magnitude of at least 10 kΩ. Thecircuitry may include at least a portion of at least one circuitselected from the group consisting of: an amplification circuit, afiltering circuit, and an analog-to-digital conversion circuit. Thecapacitive EMG sensor may further include a ground electrode to in useresistively couple to the user's skin, wherein the ground electrodeincludes a plate of electrically conductive material, and wherein theground electrode is communicatively coupled to the circuitry. Thecircuitry may include: a high-pass filter that includes the firstcapacitor and a second resistor; and a low-pass filter that includes thefirst resistor and a second capacitor.

The first sensor electrode may comprise: a first layer of a firstelectrically conductive material; and a second layer of a secondelectrically conductive material. The first electrically conductivematerial may include copper. The second electrically conductive materialmay include at least one material selected from the group consisting of:gold, steel, stainless steel, silver, titanium, electrically conductiverubber, and electrically conductive silicone. The capacitive EMG sensormay further include a housing, wherein the circuitry, the firstcapacitor, and the first layer of the first sensor electrode are allsubstantially contained within the housing, the housing including ahole, and wherein at least a portion of the second layer of the firstsensor electrode extends out of the housing through the hole. Thecapacitive EMG sensor may be a differential capacitive EMG sensor thatfurther includes: a second sensor electrode to in use resistively coupleto the user's skin, wherein the second sensor electrode includes a plateof electrically conductive material; and a second capacitor to in usegalvanically isolate the circuitry from the user's skin, the secondcapacitor electrically coupled in series between the second sensorelectrode and the circuitry.

A wearable electromyography (“EMG”) device may be summarized asincluding: at least one capacitive EMG sensor responsive to (i.e., todetect and provide at least one signal in response to detecting) muscleactivity corresponding to a gesture performed by a user of the wearableEMG device, wherein in response to muscle activity corresponding to agesture performed by a user the at least one capacitive EMG sensorprovides signals, and wherein the at least one capacitive EMG sensorincludes: a first sensor electrode to in use resistively couple to theuser's skin, wherein the first sensor electrode includes a plate ofelectrically conductive material; circuitry communicatively coupled tothe first sensor electrode of the capacitive EMG sensor; and a firstcapacitor to in use galvanically isolate the circuitry from the user'sskin, the first capacitor electrically coupled in series between thefirst sensor electrode and the circuitry; a processor communicativelycoupled to the at least one capacitive EMG sensor to in use processsignals provided by the at least one capacitive EMG sensor; and anoutput terminal communicatively coupled to the processor to transmitsignals output by the processor.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

In the drawings, identical reference numbers identify similar elementsor acts. The sizes and relative positions of elements in the drawingsare not necessarily drawn to scale. For example, the shapes of variouselements and angles are not drawn to scale, and some of these elementsare arbitrarily enlarged and positioned to improve drawing legibility.Further, the particular shapes of the elements as drawn are not intendedto convey any information regarding the actual shape of the particularelements, and have been solely selected for ease of recognition in thedrawings.

FIG. 1 is a schematic diagram of a capacitive EMG sensor that employssensor electrodes that are configured to capacitively couple to the skinof a user.

FIG. 2 is a schematic diagram of a capacitive EMG sensor employingsensor electrodes that are adapted to, in use, resistively couple to theskin of a user in accordance with the present systems, articles, andmethods.

FIG. 3 is a cross sectional view of a capacitive EMG sensor thatresistively couples to the user's skin in accordance with the presentsystems, articles, and methods.

FIG. 4 is a cross sectional view of a capacitive EMG sensor packaged ina housing and employing bi-layer sensor electrodes that protrude fromthe housing in order to physically contact and electrically couple to auser's skin in accordance with the present systems, articles, andmethods.

FIG. 5 is a flow-diagram of a method of fabricating an EMG sensor inaccordance with the present systems, articles, and methods.

FIG. 6 is a perspective view of an exemplary wearable EMG device thatincludes capacitive EMG sensors adapted to, in use, resistively coupleto the user's skin in accordance with the present systems, articles, andmethods.

DETAILED DESCRIPTION

In the following description, certain specific details are set forth inorder to provide a thorough understanding of various disclosedembodiments. However, one skilled in the relevant art will recognizethat embodiments may be practiced without one or more of these specificdetails, or with other methods, components, materials, etc. In otherinstances, well-known structures associated with electric circuits, andin particular printed circuit boards, have not been shown or describedin detail to avoid unnecessarily obscuring descriptions of theembodiments.

Unless the context requires otherwise, throughout the specification andclaims which follow, the word “comprise” and variations thereof, suchas, “comprises” and “comprising” are to be construed in an open,inclusive sense, that is as “including, but not limited to.”

Reference throughout this specification to “one embodiment” or “anembodiment” means that a particular feature, structures, orcharacteristics may be combined in any suitable manner in one or moreembodiments.

As used in this specification and the appended claims, the singularforms “a,” “an,” and “the” include plural referents unless the contentclearly dictates otherwise. It should also be noted that the term “or”is generally employed in its broadest sense, that is as meaning “and/or”unless the content clearly dictates otherwise.

The headings and Abstract of the Disclosure provided herein are forconvenience only and do not interpret the scope or meaning of theembodiments.

The various embodiments described herein provide systems, articles, andmethods for surface EMG sensors that improve upon existing resistive andcapacitive EMG sensor designs. The surface EMG sensors described hereinmay be understood as hybrid surface EMG sensors that incorporateelements from both resistive EMG sensors and capacitive EMG sensors. Inparticular, the present systems, articles, and methods describecapacitive EMG sensors that employ at least one sensor electrode thatresistively couples to the user's body (e.g., skin) and at least onediscrete component capacitor that interrupts the signal path between theat least one sensor electrode and the sensor circuitry. In this way, thecapacitive element of the capacitive EMG sensor remains but isessentially moved downstream in the sensor circuit, affording manybenefits discussed in detail below. An example application in a wearableEMG device that forms part of a human-electronics interface is alsodescribed.

Throughout this specification and the appended claims, the term“capacitive EMG sensor” is used to describe a surface EMG sensor inwhich communicative coupling between the user's body (e.g., skin) andthe sensor circuitry is mediated by at least one capacitive element suchthat the sensor circuitry is galvanically isolated from the body of theuser. In the art, this at least one capacitive element is typicallyrealized at the sensor electrode by configuring the sensor electrode tocapacitively couple to the user's skin (e.g., by coating theelectrically conductive plate of the sensor electrode with a thin layerof dielectric material). In accordance with the present systems,articles, and methods, the at least one capacitive element may be moveddownstream in the sensor such that the sensor electroderesistively/galvanically couples to the user's skin but at least onediscrete component capacitor mediates communicative coupling between thesensor electrode and the sensor circuitry.

For comparison purposes, the elements of a capacitive EMG sensor thatimplements a sensor electrode that capacitively couples to the user'sskin are first described.

FIG. 1 is a schematic diagram of a capacitive EMG sensor 100 thatemploys sensor electrodes 101 a, 101 b that are configured tocapacitively couple to the skin of a user. Sensor 100 is a differentialcapacitive EMG sensor that employs two sensor electrodes 101 a, 101 b asdescribed in, for example, U.S. Provisional Patent Application Ser. No.61/771,500 (now U.S. Non-Provisional patent application Ser. No.14/194,252) which is incorporated by reference herein in its entirety.However, a person of skill in the art will appreciate that the basicdescription of sensor 100 herein is also applicable to single-endedsensor systems that employ only a single sensor electrode (i.e., one ofsensor electrodes 101 a or 101 b). Sensor electrodes 101 a and 101 beach comprise a respective electrically conductive plate 171 a, 171 bcoated with a respective layer of dielectric material 172 a, 172 b.Sensor 100 also includes a ground electrode 140 that comprises anelectrically conductive plate that is exposed (i.e., not coated withdielectric material) so that ground electrode 140 resistively couples tothe user's skin as described in U.S. Provisional Patent Application Ser.No. 61/903,238 (now U.S. Non-Provisional patent application Ser. No.14/539,773), which is incorporated herein by reference in its entirety.

Sensor 100 includes circuitry that comprises, at least: electricallyconductive pathways 111 a, 111 b, 112, 113 a, 113 b; resistors 130 a,130 b; and amplifier 150. First sensor electrode 101 a iscommunicatively coupled to amplifier 150 through electrically conductivepathway 111 a and to ground electrode 140 through a path that compriseselectrically conductive pathway 113 a, resistor 130 a, and electricallyconductive pathway 112. Second sensor electrode 101 b is communicativelycoupled to amplifier 150 through electrically conductive pathway 111 band to ground electrode 140 through a path that comprises electricallyconductive pathway 113 b, resistor 130 b, and electrically conductivepathway 112.

Sensor 100 is a capacitive EMG sensor in the traditional sense becauseit implements sensor electrodes 101 a, 101 b that are configured tocapacitively couple to the skin of the user. Amplifier 150 isgalvanically isolated from the user's skin by the dielectric layers 172a, 172 b that coat sensor electrodes 101 a, 101 b, respectively. Asdiscussed previously, this galvanic isolation is advantageous, at leastbecause it prevents DC voltage(s) from coupling to amplifier 150 andprevents voltage(s) from being applied to the user's skin. However, thecapacitive coupling to the skin through sensor electrodes 101 a, 101 bintroduces a relatively large impedance between the user's skin andamplifier 150. This impedance imposes stringent requirements onamplifier 150 and, ultimately, increases the cost of amplifier 150 insensor 100. Furthermore, the magnitude of the capacitive couplingbetween sensor electrodes 101 a, 101 b and the user's skin is highlydependent on parameters such as skin conductance, skin moisture/sweatlevels, hair density, and so on, all of which can vary considerably fromuser to user (and even in different scenarios for the same user, such asat different levels of physical activity). Thus, even though thegalvanic isolation realized by dielectric layers 172 a and 172 b isdesirable in a surface EMG sensor, capacitive coupling between sensorelectrodes 101 a, 101 b and the user's skin has undesirableconsequences. In accordance with the present systems, articles, andmethods, the benefits of galvanically isolating the amplifier (e.g.,150) from the user's skin may be realized without the drawbacks ofcapacitively coupling the sensor electrode(s) to the user's skin by acapacitive EMG sensor design in which the capacitive interruptionbetween the user's skin and the amplifier is moved downstream in thesensor circuit and realized by a discrete component capacitor coupled inbetween a resistive sensor electrode and an amplification circuit.

FIG. 2 is a schematic diagram of a capacitive EMG sensor 200 employingsensor electrodes 201 a, 201 b that are adapted to, in use, resistivelycouple to the body (e.g., skin) of a user in accordance with the presentsystems, articles, and methods. Each of sensor electrodes 201 a and 201b comprises a respective plate of electrically conductive material, butunlike electrodes 101 a and 101 b from sensor 100, electrodes 201 a and201 b are not coated with dielectric material. Instead, each ofelectrodes 201 a and 201 b includes a respective bare/exposedelectrically conductive surface to directly physically contact theuser's skin during use. Thus, capacitive EMG sensor 200 implementssensor electrodes 201 a, 201 b that resemble the sensor electrodes thatwould typically be found in a resistive EMG sensor. However, inaccordance with the present systems, articles, and methods, sensor 200is still a capacitive EMG sensor because sensor 200 includes discretecomponent capacitors 221 a and 221 b that galvanically isolate the restof the sensor circuitry from the user's body (e.g., skin).

Sensor 200 is illustrated as a differential capacitive EMG sensor thatemploys a first sensor electrode 201 a and a second sensor electrode 201b, though a person of skill in the art will appreciate that thedescription of sensor 200 herein is also applicable to single-endedsensor systems that employ only a single sensor electrode (i.e., one ofsensor electrodes 201 a or 201 b).

Sensor 200 includes an amplification circuit (i.e., an amplifier) 250.First sensor electrode 201 a is communicatively coupled to amplifier 250by a first electrically conductive pathway 211 a. A first capacitor 221a is electrically coupled in series between first sensor electrode 201 aand amplifier 250 in first electrically conductive pathway 211 a. Firstcapacitor 221 a galvanically isolates amplifier 250 from the user's body(e.g., skin) and thereby affords some of the benefits typicallyassociated with a capacitive EMG sensor (i.e., capacitor 221 a preventsDC voltage(s) from coupling to amplifier 250 and prevents voltage(s)from being applied to the user's skin). While a traditional capacitiveEMG sensor achieves this galvanic isolation by capacitively coupling tothe user's skin at the sensor electrode (e.g., as per sensor electrode101 a from sensor 100), in sensor 200 electrode 201 a is resistivelycoupled to the user's skin and galvanic isolation is moved downstream todiscrete component capacitor 221 a. As previously described, resistivecoupling to the user's skin as per electrode 201 a from sensor 200provides a lower impedance between the user's skin and amplifier 250than capacitive coupling to the user's skin as in electrode 101 a fromsensor 100, and this lower impedance simplifies and lowers the cost ofamplifier 250 in sensor 200 compared to amplifier 150 in sensor 100.Furthermore, because capacitor 221 a is a discrete component, themagnitude of its capacitance can be selected and will remain essentiallyconstant from user to user, regardless of variations such as skinconductance, moisture/sweat levels, hair density, and so on. An exampleimplementation may employ, as capacitors 221 a (and similarly ascapacitor 221 b), a discrete component capacitor having a magnitude ofabout 100 nF. Typical capacitive coupling between a dielectric-coatedcEMG sensor and a user's skin is significantly less than this, thus 100nF may dominate the range of variations in skin:electrode capacitancetypically seen in cEMG across different users and/or use conditions. Theincorporation of a discrete component capacitor 221 a in lieu ofcondition-dependent capacitive coupling between the electrode and theuser's skin is very easy and inexpensive to manufacture and provides anessentially fixed capacitance to which the rest of the sensor circuitrymay be tuned for improved performance.

In addition to first capacitor 221 a, sensor 200 also includes a firstresistor 231 a that is electrically coupled in series between firstsensor electrode 201 a and amplifier 250 in first electricallyconductive pathway 211 a. Similar to first capacitor 221 a, firstresistor 231 a may be a discrete electronic component with a magnitudethat can be selected, accurately embodied, and held substantiallyconstant during use. In the illustrated example of FIG. 2, firstcapacitor 221 a and first resistor 231 a are electrically coupled inseries with one another in first electrically conductive pathway 211 a.First resistor 231 a is included, at least in part, to dominate theimpedance between electrode 201 a and the user's skin such thatvariations in the impedance between electrode 201 a and the user's skindue to fluctuations in skin and/or environmental conditions (e.g., skinconductance, moisture/sweat levels, hair density, etc.) are renderedessentially negligible. For example, fluctuations in skin and/orenvironmental conditions may cause the impedance between electrode 201 aand the user's skin to vary by a magnitude of on the order of 1Ω, 10Ω,100Ω, or 1000Ω, but first resistor 231 a may be selected to have aresistance of on the order of at least 1 kΩ, at least 10 kΩ, at least100 kΩ, or more such that the impedance of first resistor 231 adominates the impedance (and, more specifically, dominates variations inthe impedance) between sensor electrode 201 a and the user's skin. Thesensor circuitry, including amplifier 250, may be tuned to accommodatethe relatively large impedance of first resistor 231 a such that therelatively small variations in the impedance between sensor electrode201 a and the user's skin from user to user (and/or under different useconditions for the same user) have a diminished effect on theperformance of sensor 200. First resistor 231 a also serves to limitcurrent into amplifier 250 and thereby improves the ESD protection ofamplifier 250.

The amplifier(s) used in the capacitive EMG sensors described herein mayinclude one or more of various types of amplifier(s), including one ormore instrumentation amplifier(s) and/or one or more single or dualoperational amplifier(s), depending, for example, on whether the EMGsensor is single-ended or differential. As sensor 200 is differential,amplifier 250 may include a dual operational amplifier (e.g., a“two-op-amp instrumentation amplifier”) such as the MAX9916 or theMAX9917, both available from Maxim Integrated, or any of various otheramplifier configurations, including but not limited to amplifiersembodied in integrated circuits. A person of skill in the art willappreciate that the output(s) and/or some of the inputs of amplifier 250may be connected through various resistor configurations for at leastthe purpose of determining the gain of amplifier 250.

Sensor 200 includes a second electrically conductive pathway 212 thatcommunicatively couples to ground through a ground electrode 240. Groundelectrode 240 comprises a plate of electrically conductive material thatresistively couples to the user's skin. As sensor 200 is differential,ground electrode 240 may not necessarily be used as a referencepotential but may primarily provide a path for electrical currents toreturn to the user's body (e.g., skin). Using second electricallyconductive pathway 212, together with first capacitor 221 a and firstresistor 231 a, circuitry connected to first sensor electrode 201 a alsoincludes both a low-pass filtering configuration and a high-passfiltering configuration “in front of” or upstream of amplifier 250 in adirection in which signals pass. Specifically, sensor 200 includes athird electrically conductive pathway 213 a that communicatively couplesfirst electrically conductive pathway 211 a and second electricallyconductive pathway 212. Third electrically conductive pathway 213 aincludes a second capacitor 222 a electrically coupled in between firstelectrically conductive pathway 211 a and second electrically conductivepathway 212. The configuration of first resistor 231 a and secondcapacitor 222 a (with respect to sensor electrode 201 a, amplifier 250,and ground electrode 240) forms a low-pass filtering circuit. As anexample, when first resistor 231 a has a magnitude of about 100 kΩ,second capacitor 222 a may have a magnitude of about 10 pF in order toprovide desirable low-pass filtering performance. Similarly, sensor 200includes a fourth electrically conductive pathway 214 a thatcommunicatively couples first electrically conductive pathway 211 a andsecond electrically conductive pathway 212. Fourth electricallyconductive pathway 214 a includes a second resistor 232 a electricallycoupled in between first electrically conductive pathway 211 a andsecond electrically conductive pathway 212. The configuration of firstcapacitor 221 a and second resistor 232 a (with respect to sensorelectrode 201 a, amplifier 250, and ground electrode 240) forms ahigh-pass filtering circuit.

In comparing sensor 200 from FIG. 2 to sensor 100 from FIG. 1, secondresistor 232 a in sensor 200 is similar in position and function toresistor 130 a in sensor 100. The magnitude of a resistor in thisposition (i.e., the magnitude of second resistor 232 a in sensor 200 orresistor 130 a in sensor 100) directly influences the filteringperformance of the corresponding high-pass filter; however, as themagnitude of a resistor in this position increases, the stability of thecircuit may degrade and more noise may appear. This introduces a furtherbenefit of first capacitor 221 a in sensor 200: first capacitor 221 acompensates for a decrease in the magnitude of second resistor 232 a andthereby allows a lower-magnitude resistor to be used for second resistor232 a in sensor 200 compared to resistor 130 a in sensor 100. The lowermagnitude of second resistor 232 a in sensor 200 compared to resistor130 a in sensor 100 results in both reduced noise and enhanced stabilityin sensor 200 compared to sensor 100. As an example, second resistor 232a may have a magnitude of about 10 MΩ or less (e.g., about 1 MΩ) andfirst capacitor 221 a may have a magnitude of about 100 nF.

As previously described, the illustrated example in FIG. 2 of capacitiveEMG sensor 200 is a differential capacitive EMG sensor. To this end,sensor 200 includes: a second sensor electrode 201 b that issubstantially similar to first sensor electrode 201 a; a fifthelectrically conductive pathway 211 b (analogous to first electricallyconductive pathway 211 a) that communicatively couples second sensorelectrode 201 b to amplifier 250; a third capacitor 221 b (analogous tofirst capacitor 221 a) electrically coupled in series between secondsensor electrode 201 b and amplifier 250 in fifth electricallyconductive pathway 211 b; and a third resistor 231 b (analogous to firstresistor 231 a) electrically coupled in series between second sensorelectrode 201 b and amplifier 250 in fifth electrically conductivepathway 211 b. In the illustrated example of FIG. 2, third capacitor 221b and third resistor 231 b are electrically coupled in series with oneanother in fifth electrically conductive pathway 211 b. Third capacitor221 b may be substantially similar to first capacitor 221 a and thirdresistor 231 b may be substantially similar to first resistor 231 a.Sensor 200 also includes: a sixth electrically conductive pathway 213 b(analogous to third electrically conductive pathway 213 a) thatcommunicatively couples fifth electrically conductive pathway 211 b andsecond electrically conductive pathway 212; a fourth capacitor 222 b(analogous to third capacitor 222 a) electrically coupled in sixthelectrically conductive pathway 213 b in between fifth electricallyconductive pathway 211 b and second electrically conductive pathway 212;a seventh electrically conductive pathway 214 b (analogous to fourthelectrically conductive pathway 214 a) that communicatively couplesfifth electrically conductive pathway 211 b and second electricallyconductive pathway 212; and a fourth resistor 232 b (analogous to secondresistor 232 a) electrically coupled in seventh electrically conductivepathway 214 b in between fifth electrically conductive pathway 211 b andsecond electrically conductive pathway 212. Third capacitor 221 b andfourth resistor 232 b form a high-pass filter configuration with respectto sensor electrode 201 b, amplifier 250, and ground electrode 240 whilethird resistor 231 b and fourth capacitor 222 b form a low-pass filterconfiguration with respect to sensor electrode 201 b, amplifier 250, andground electrode 240. Fourth capacitor 222 b may be substantiallysimilar to second capacitor 222 a and fourth resistor 232 b may besubstantially similar to second resistor 232 a.

The various examples of capacitive EMG sensors described herein,including sensor 200 from FIG. 2, may be formed as a printed circuitboard, formed as an integrated circuit, or otherwise carried by asubstrate. In this case, one or more electrically conductive pathways(e.g., electrically conductive pathways 211 a, 211 b, 212, 213 a, 213 b,214 a, and/or 214 b) may be embodied by one or more electricallyconductive trace(s) carried by a substrate and formed using one or morelithography process(es).

FIG. 3 is a cross sectional view of a capacitive EMG sensor 300 thatresistively couples to the user's skin in accordance with the presentsystems, articles, and methods. Sensor 300 is an example of a physicalembodiment of the schematic diagram for sensor 200 shown in FIG. 2.Sensor 300 includes elements of sensor 200 and, in general, thedescriptions of the elements of sensor 200 apply to the analogouselements in sensor 300 and vice versa.

Sensor 300 includes a substrate 360 formed of an insulating material(e.g., FR-4) and having a first surface 360 a and a second surface 360b. Second surface 360 b is opposite first surface 360 a across athickness of substrate 360. Sensor 300 is a differential EMG sensorcomprising two sensor electrodes 301 a, 301 b (analogous to sensorelectrodes 201 a, 201 b of sensor 200), both carried by first surface360 a of substrate 360. The circuitry that comprises the other elementsof sensor 300 (e.g., an amplifier 350 analogous to amplifier 250 ofsensor 200, capacitors 321 a, 321 b analogous to capacitors 221 a, 221 bof sensor 200, and resistors 331 a, 331 b analogous to resistors 231 a,231 b of sensor 200) is carried by second surface 360 b of substrate 360and communicatively coupled to electrodes 301 a, 301 b by electricallyconductive pathways 311 a, 311 b (analogous to electrically conductivepathways 211 a, 211 b of sensor 200), which include via portions thatextend through the thickness of substrate 360 and electricallyconductive trace portions that are carried by second surface 360 b ofsubstrate 360.

Throughout this specification and the appended claims, the terms“carries” and “carried by” are generally used to describe a spatialrelationship in which a first layer/component is positioned proximateand physically coupled to a surface of a second layer/component, eitherdirectly or through one or more intervening layers/components. Forexample, electrode 301 a is carried by first surface 360 a of substrate360 and amplifier 350 is carried by second surface 360 b of substrate360. Amplifier 350 is directly carried by second surface 360 b ofsubstrate 360 because there are no intervening layers/components thatmediate the physical coupling between amplifier 350 and second surface360 b of substrate 360; however, amplifier 350 would still be considered“carried by” second surface 360 b of substrate 360 even if the physicalcoupling between amplifier 350 and second surface 360 b of substrate 360was mediated by at least one intervening layer/component. The terms“carries” and “carried by” are not intended to denote a particularorientation with respect to top and bottom and/or left and right.

Each resistive sensor electrode of the capacitive EMG sensors describedherein (e.g., electrodes 301 a, 301 b of sensor 300) comprises arespective electrically conductive plate that physically andelectrically (i.e., galvanically/resistively) couples to the user's skinduring use. For each such sensor electrode, the electrically conductiveplate may be formed of, for example, a material that includes copper(such as pure elemental copper or a copper alloy), deposited and etchedin accordance with established lithography techniques. While copper isan excellent material from which to form sensor electrodes 301 a, 301 bfrom a manufacturing point of view (because lithography techniques forprocessing copper are very well established in the art), an exposedsurface of pure copper will ultimately form an insulating oxide layerand/or react with the skin of a user in other undesirable ways. Thiseffect may be acceptable for traditional capacitive sensor electrodesthat capacitively couple to the user because, as described previously,such electrodes are typically coated with an insulating dielectric layeranyway. However, the formation of such an insulating layer canundesirably effect the operation of a sensor electrode that resistivelycouples to the user's skin. In some cases, a user's skin may even reactwith copper, resulting in a rash or other discomfort for the user. Forat least these reasons, in accordance with the present systems,articles, and methods it can be advantageous to form each of sensorelectrodes 301 a, 301 b (and likewise electrodes 201 a and 201 b of FIG.2) as a respective multilayer (e.g., bi-layer) structure comprising afirst layer 371 a, 371 b formed of a first electrically conductivematerial (e.g., copper or a material including copper) and at least asecond layer 372 a, 372 b formed of a second electrically conductivematerial. In accordance with the present systems, articles, and methods,the second electrically conductive material may be an inert,non-reactive, and/or biocompatible material. For example, the secondelectrically conductive material may include: gold, steel (e.g., astainless steel such as a 316 stainless steel or a low-nickel stainlesssteel to mitigate dermatological nickel allergies, such as 430 stainlesssteel), silver, titanium, electrically conductive rubber, and/orelectrically conductive silicone.

The use of multilayer (e.g., bi-layer) structures for sensor electrodes301 a, 301 b is advantageous because it enables the first layer 371 a,371 b to be formed of copper using established lithography techniquesand the second layer 372 a, 372 b to be subsequently applied in order toprotect the copper from exposure to the user/environment and to protectthe user from exposure to the copper. Furthermore, an EMG sensor (e.g.,sensor 300) may be packaged in a housing for both protective andaesthetic purposes, and a second layer 372 a, 372 b of electricallyconductive material may be used to effectively increase the thickness ofsensor electrodes 301 a, 301 b such that they protrude outwards from thehousing to resistively couple to the user's skin during use.

FIG. 4 is a cross sectional view of a capacitive EMG sensor 400 packagedin a housing 490 and employing bi-layer sensor electrodes 401 a, 401 bthat protrude from the housing in order to physically contact andelectrically (i.e., resistively/galvanically) couple to a user's skin inaccordance with the present systems, articles, and methods. Sensor 400is substantially similar to sensor 300 from FIG. 3 and includes the sameor similar elements (e.g., a substrate 460 having a first surface 460 aand a second surface 460 b, where first surface 460 a carries first andsecond sensor electrodes 401 a, 401 b and second surface 460 b carriesan amplifier 450, first and second capacitors 421 a, 421 b, first andsecond resistors 431 a, 431 b, etc.), all at least partially containedwithin the inner volume of a housing 490. Housing 490 may be formed ofsubstantially rigid material. Throughout this specification and theappended claims, the term “rigid” as in, for example, “substantiallyrigid material,” is used to describe a material that has an inherenttendency to maintain or restore its shape and resistmalformation/deformation under, for example, the moderate stresses andstrains typically encountered by a wearable electronic device.

Bi-layer sensor electrodes 401 a, 401 b are similar to bi-layer sensorelectrodes 301 a, 301 b of sensor 300 in that they each comprise arespective first layer 471 a, 471 b formed of a first electricallyconductive material (e.g., copper, or a material including copper) and arespective second layer 472 a, 472 b formed of a second electricallyconductive material (e.g., gold, steel, stainless steel, conductiverubber, etc.); however, in sensor 400 the respective second layer 472 a,472 b of each of electrodes 401 a, 401 b is substantially thicker thanthe respective first layer 471 a, 471 b of each of electrodes 401 a, 401b. At least two holes 480 a, 480 b in housing 490 provide access to theinner volume of housing 490, and the thickness of second layers 472 a,472 b of electrodes 401 a, 401 b (respectively) is sufficient such thatat least respective portions of second layers 472 a, 472 b protrude outof housing 490 through holes 480 a, 480 b. More specifically, firstsensor electrode 401 a includes a first layer 471 a and a second layer472 a, housing 490 includes a first hole 480 a, and at least a portionof second layer 472 a of first sensor electrode 401 a extends out ofhousing 490 through first hole 480 a. Likewise, second sensor electrode401 b includes a first layer 471 b and a second layer 472 b, housing 490includes a second hole 480 b, and at least a portion of second layer 472b of second sensor electrode 401 b extends out of housing 490 throughsecond hole 480 b. In this way, housing 490 protects sensor 400 from theelements and affords opportunities to enhance aesthetic appeal, whilethe protruding portions of second layers 472 a, 472 b of sensorelectrodes 401 a, 401 b are still able to resistively couple to the skinof the user during use. Housing 490 also helps to electrically insulateelectrodes 401 a, 401 b from one another. In some applications, it canbe advantageous to seal any gap between the perimeter of first hole 480a and the protruding portion of second layer 472 a of first electrode401 a (using, e.g., a gasket, an epoxy or other sealant or, in the caseof electrically conductive rubber or electrically conductive silicone asthe material forming second layer 472 a of first electrode 401 a, atight interference fit between the perimeter of first hole 480 a and theprotruding portion of second layer 472 a of first electrode 401 a) toprevent moisture or contaminants from entering housing 490. Likewise, itcan be advantageous to seal any gap between the perimeter of second hole480 b and the protruding portion of second layer 472 b of secondelectrode 401 b.

As previously described, the various embodiments of capacitive EMGsensors described herein may include at least one ground electrode. Forexample, sensor 200 from FIG. 2 depicts ground electrode 240. Sensor 300from FIG. 3 and sensor 400 from FIG. 4 each do not illustrate a groundelectrode for two reasons: a) to reduce clutter; and b) because invarious embodiments, a ground electrode may or may not be carried by thesame substrate as the sensor electrode(s). Sensor electrodes (such aselectrodes 201 a, 201 b, 301 a, 301 b, and 401 a, 401 b) areadvantageously positioned near muscle groups in order to detect EMGsignals therefrom, but in some applications it is advantageous forground electrodes (such as electrode 240) to be positioned distant fromthe sensor electrodes and/or near bone instead of near muscle groups.For this reason, one or more ground electrode(s) may, in someapplications, be separate from the substrate which carries the sensorelectrodes but still communicatively coupled to the sensor circuitry byone or more electrically conductive pathways (e.g., electrical wires).However, in some applications one or more ground electrode(s) may becarried by the same substrate that carries the sensor electrodes, atleast in part because doing so greatly simplifies the design andmanufacture of the EMG sensor. For example, sensor 300 from FIG. 3 mayfurther include a ground electrode carried by first surface 360 a ofsubstrate 360 and/or sensor 400 from FIG. 4 may further include a groundelectrode carried by first surface 460 a of substrate 460. In eithercase, the ground electrode may comprise a first layer formed of a firstelectrically conductive material (e.g., copper, or a material includingcopper) and a second layer formed of a second electrically conductivematerial (e.g., gold, steel, stainless steel, electrically conductiverubber, etc.). In applications that employ a housing, such as housing490 of sensor 400, the housing may include a hole (e.g., a third hole)and at least a portion of the second layer of the ground electrode mayprotrude through the hole to physically contact and electrically (i.e.,resistively/galvanically) couple to the skin of the user during use.

In accordance with the present systems, articles, and methods,multilayer (e.g., bi-layer) electrodes, including multilayer sensorelectrodes and/or multilayer ground electrodes, may be formed by, forexample: electroplating a second layer of electrically conductivematerial on a first layer of electrically conductive material;depositing a second layer of electrically conductive material on a firstlayer of electrically conductive material using deposition or growthtechniques such as chemical vapor deposition, physical vapor depositionthermal oxidation, or epitaxy; adhering a second layer of electricallyconductive material to a first layer of electrically conductive materialusing, for example, an electrically conductive epoxy or an electricallyconductive solder; pressing a second layer of electrically conductivematerial against a first layer of electrically conductive materialusing, for example, an interference fit, one or more spring(s), or oneor more elastic band(s); or otherwise generally bonding a secondelectrically conductive material to a first electrically conductivematerial in such a way that the second electrically conductive materialis electrically coupled to the first electrically coupled material.

FIG. 5 is a flow-diagram of a method 500 of fabricating an EMG sensor inaccordance with the present systems, articles, and methods. Method 500includes five acts 501, 502, 503, 504, and 505, though those of skill inthe art will appreciate that in alternative embodiments certain acts maybe omitted and/or additional acts may be added. Those of skill in theart will also appreciate that the illustrated order of the acts is shownfor exemplary purposes only and may change in alternative embodiments.

At 501, a first sensor electrode is formed on a first surface of asubstrate. The first sensor electrode may comprise an electricallyconductive plate such as for example electrode 301 a of sensor 300 orelectrode 401 a of sensor 400, formed using, as an example, lithographytechniques. The first sensor electrode may include a single layer ofelectrically conductive material or multiple (i.e., at least two) layersof one or more electrically conductive material(s). Forming the firstsensor electrode may therefore include depositing at least a first layerof a first electrically conductive material (e.g., copper) on the firstsurface of the substrate. Where, in accordance with the present systems,articles, and methods, it is desirable for the first sensor electrode tocomprise multiple layers, forming the first sensor electrode may furtherinclude depositing a second layer of a second electrically conductivematerial (e.g., gold, steel, stainless steel, electrically conductiverubber, etc.) on the first layer of the first electrically conductivematerial (either directly by, for example, a plating process orindirectly by, for example, employing an intervening adhesive layer suchas an electrically conductive epoxy or an electrically conductivesolder).

At 502, an amplifier (e.g., amplifier 250 of sensor 200, amplifier 350of sensor 300, or amplifier 450 of sensor 400) is deposited on a secondsurface of the substrate. The amplifier may include an amplificationcircuit and/or one or more discrete electronic component amplifier(s),such as for example on or more operational amplifier(s), differentialamplifier(s), and/or instrumentation amplifier(s). Depositing theamplifier on the second surface of the substrate may include soldering adiscrete component amplifier to one or more electrically conductivetrace(s) and/or bonding pad(s) carried by the second surface of thesubstrate (i.e., soldering the amplifier on the second surface of thesubstrate using, for example, a surface-mount technology, or “SMT,”process).

At 503, a first capacitor (e.g., capacitor 221 a of sensor 200,capacitor 321 a of sensor 300, or capacitor 421 a of sensor 400) isdeposited on the second surface of the substrate. The first capacitormay include a discrete electronic component capacitor and depositing thefirst capacitor on the second surface of the substrate may includesoldering the first capacitor to one or more electrically conductivetrace(s) and/or bonding pad(s) carried by the second surface of thesubstrate (i.e., soldering the first capacitor on the second surface ofthe substrate using, for example, a SMT process).

At 504, a first resistor (e.g., resistor 231 a of sensor 200, resistor331 a of sensor 300, or resistor 431 a of sensor 400) is deposited onthe second surface of the substrate. The first resistor may include adiscrete electronic component resistor and depositing the first resistoron the second surface of the substrate may include soldering the firstresistor to one or more electrically conductive trace(s) and/or bondingpad(s) carried by the second surface of the substrate (i.e., solderingthe first resistor on the second surface of the substrate using, forexample, a SMT process).

As described previously, a person of skill in the art will appreciatethat the order of the acts in method 500, and in particular the order ofacts 501, 502, 503, and 504, is provided as an example only and inpractice acts 501, 502, 503, and 504 may be carried out in virtually anyorder or combination, and any/all of acts 501, 502, 503, and 504 may becarried out substantially concurrently or even simultaneously (in, forexample, an SMT process).

At 505, a first electrically conductive pathway (e.g., pathway 211 a ofsensor 200 or pathway 311 a of sensor 300) that communicatively couplesthe first sensor electrode to the amplifier through the first capacitorand the first resistor is formed. The first electrically conductivepathway may include one or more section(s) of electrically conductivetrace carried by the second surface of the substrate and at least onevia that electrically couples at least one of the one or more section(s)of electrically conductive trace to the first sensor electrode carriedby the first surface of the substrate. Thus, forming the firstelectrically conductive pathway may employ established lithographytechniques to form the one or more section(s) of electrically conductivetrace and to form a via through the substrate.

As previously described, the EMG sensor may include or otherwise bepackaged in a housing, such as housing 490 of sensor 400. In this case,method 500 may be extended to include enclosing the substrate in ahousing. Enclosing the substrate in the housing includes enclosing theamplifier, the first capacitor, and the first resistor in the housing.The housing may include a hole providing access to the inner volumethereof, and enclosing the substrate in the housing may include aligningthe first sensor electrode with the hole so that at least a portion ofthe first senor electrode protrudes out of the housing through the hole.For implementations in which the first sensor electrode comprises afirst layer and a second layer, aligning the first sensor electrode withthe hole may include aligning the first sensor electrode with the holeso that at least a portion of the second layer protrudes out of thehousing through the hole.

As previously described, the EMG sensor may include a ground electrode.For example, sensor 200 from FIG. 2 includes ground electrode 240. Inorder to include a ground electrode (240) and associated circuitry in anEMG sensor, method 500 may be extended to include: forming the groundelectrode (240) on the first surface of the substrate; forming a secondelectrically conductive pathway (212) that communicatively couples tothe ground electrode (240); depositing a second capacitor (222 a) on thesecond surface of the substrate; forming a third electrically conductivepathway (213 a) that communicatively couples the first electricallyconductive pathway (211 a) and the second electrically conductivepathway (212) through the second capacitor (222 a); depositing a secondresistor (232 a) on the second surface of the substrate; and forming afourth electrically conductive pathway (214 a) that communicativelycouples the first electrically conductive pathway (211 a) and the secondelectrically conductive pathway (212) through the second resistor (232a). Forming the ground electrode and the second, third, and fourthelectrically conductive pathways may employ established lithographyprocesses. Depositing the second capacitor and the second resistor mayinvolve soldering discrete circuit components on the substrate (e.g.,using a SMT process).

With or without a ground electrode (240), the EMG sensor may bedifferential. For example, sensor 200 from FIG. 2 includes second sensorelectrode 201 b. In order to include a second sensor electrode (201 b)and associated circuitry in an EMG sensor, method 500 may be extended toinclude: forming a second sensor electrode (201 b) on the first surfaceof the substrate; depositing a third capacitor (221 b) on the secondsurface of the substrate; depositing a third resistor (231 b) on thesecond surface of the substrate; and forming a fifth electricallyconductive pathway (211 b) that communicatively couples the secondsensor electrode (201 b) and the amplifier (250) through the thirdcapacitor (221 b) and the third resistor (231 b). Forming the secondsensor electrode and the fifth electrically conductive pathway mayemploy established lithography processes. Depositing the third capacitorand the third resistor may involve soldering discrete circuit componentson the substrate (e.g., using a SMT process). For a differential EMGsensor that includes a ground electrode (e.g., as in sensor 200 fromFIG. 2), method 500 may be extended to include: depositing a fourthcapacitor (222 b) on the second surface of the substrate; forming asixth electrically conductive pathway (213 b) that communicativelycouples the fifth electrically conductive pathway (211 b) and the secondelectrically conductive pathway (212) through the fourth capacitor (222b); depositing a fourth resistor (232 b) on the second surface of thesubstrate; and forming a seventh electrically conductive pathway (214 b)that communicatively couples the fifth electrically conductive pathway(211 b) and the second electrically conductive pathway (212) through thefourth resistor (232 b). Forming the sixth and seventh electricallyconductive pathways may employ established lithography processes.Depositing the fourth capacitor and the fourth resistor may involvesoldering discrete circuit components on the substrate (e.g., using aSMT process).

Capacitive EMG sensors having sensor electrodes that resistively coupleto the user's skin as described herein may be implemented in virtuallyany system, device, or process that makes use of capacitive EMG sensors;however, the capacitive EMG sensors described herein are particularlywell-suited for use in EMG devices that are intended to be worn by (orotherwise coupled to) a user for an extended period of time and/or for arange of different skin and/or environmental conditions. As an example,the capacitive EMG sensors described herein may be implemented in awearable EMG device that provides gesture-based control in ahuman-electronics interface. Some details of exemplary wearable EMGdevices that may be adapted to include at least one capacitive

EMG sensor from the present systems, articles, and methods are describedin, for example, U.S. Provisional Patent Application Ser. No. 61/768,322(now U.S. Non-Provisional patent application Ser. No. 14/186,889); U.S.Provisional Patent Application Ser. No. 61/857,105 (now U.S.Non-Provisional patent application Ser. No. 14/335,668); U.S.Provisional Patent Application Ser. No. 61/860,063 (now U.S.Non-Provisional patent application Ser. No. 14/276,575); U.S.Provisional Patent Application Ser. No. 61/866,960 (now U.S.Non-Provisional patent application Ser. No. 14/461,044); U.S.Provisional Patent Application Ser. No. 61/869,526 (now U.S.Non-Provisional patent application Ser. No. 14/465,194); U.S.Provisional Patent Application Ser. No. 61/881,064 (now U.S.Non-Provisional patent application Ser. No. 14/494,274); and U.S.Provisional Patent Application Ser. No. 61/894,263 (now U.S.Non-Provisional patent application Ser. No. 14/520,081), all of whichare incorporated herein by reference in their entirety.

Throughout this specification and the appended claims, the term“gesture” is used to generally refer to a physical action (e.g., amovement, a stretch, a flex, a pose, etc.) performed or otherwiseeffected by a user. Any physical action performed or otherwise effectedby a user that involves detectable muscle activity (detectable, e.g., byat least one appropriately positioned EMG sensor) may constitute agesture in the present systems, articles, and methods.

FIG. 6 is a perspective view of an exemplary wearable EMG device 600that includes capacitive EMG sensors adapted to, in use, resistivelycouple to the user's skin in accordance with the present systems,articles, and methods. Exemplary wearable EMG device 600 may, forexample, form part of a human-electronics interface. Exemplary wearableEMG device 600 is an armband designed to be worn on the forearm of auser, though a person of skill in the art will appreciate that theteachings described herein may readily be applied in wearable EMGdevices designed to be worn elsewhere on the body of the user, includingwithout limitation: on the upper arm, wrist, hand, finger, leg, foot,torso, or neck of the user.

Device 600 includes a set of eight pod structures 601, 602, 603, 604,605, 606, 607, and 608 that form physically coupled links of thewearable EMG device 600. Each pod structure in the set of eight podstructures 601, 602, 603, 604, 605, 606, 607, and 608 is positionedadjacent and in between two other pod structures in the set of eight podstructures such that the set of pod structures forms a perimeter of anannular or closed loop configuration. For example, pod structure 601 ispositioned adjacent and in between pod structures 602 and 608 at leastapproximately on a perimeter of the annular or closed loop configurationof pod structures, pod structure 602 is positioned adjacent and inbetween pod structures 601 and 603 at least approximately on theperimeter of the annular or closed loop configuration, pod structure 603is positioned adjacent and in between pod structures 602 and 604 atleast approximately on the perimeter of the annular or closed loopconfiguration, and so on. Each of pod structures 601, 602, 603, 604,605, 606, 607, and 608 is physically coupled to the two adjacent podstructures by at least one adaptive coupler (not visible in FIG. 6). Forexample, pod structure 601 is physically coupled to pod structure 608 byan adaptive coupler and to pod structure 602 by an adaptive coupler. Theterm “adaptive coupler” is used throughout this specification and theappended claims to denote a system, article or device that providesflexible, adjustable, modifiable, extendable, extensible, or otherwise“adaptive” physical coupling. Adaptive coupling is physical couplingbetween two objects that permits limited motion of the two objectsrelative to one another. An example of an adaptive coupler is an elasticmaterial such as an elastic band. Thus, each of pod structures 601, 602,603, 604, 605, 606, 607, and 608 in the set of eight pod structures maybe adaptively physically coupled to the two adjacent pod structures byat least one elastic band. The set of eight pod structures may bephysically bound in the annular or closed loop configuration by a singleelastic band that couples over or through all pod structures or bymultiple separate elastic bands that couple between adjacent pairs ofpod structures or between groups of adjacent pairs of pod structures.Device 600 is depicted in FIG. 6 with the at least one adaptive couplercompletely retracted and contained within the eight pod structures 601,602, 603, 604, 605, 606, 607, and 608 (and therefore the at least oneadaptive coupler is not visible in FIG. 6).

Throughout this specification and the appended claims, the term “podstructure” is used to refer to an individual link, segment, pod,section, structure, component, etc. of a wearable EMG device. For thepurposes of the present systems, articles, and methods, an “individuallink, segment, pod, section, structure, component, etc.” (i.e., a “podstructure”) of a wearable EMG device is characterized by its ability tobe moved or displaced relative to another link, segment, pod, section,structure component, etc. of the wearable EMG device. For example, podstructures 601 and 602 of device 600 can each be moved or displacedrelative to one another within the constraints imposed by the adaptivecoupler providing adaptive physical coupling therebetween. The desirefor pod structures 601 and 602 to be movable/displaceable relative toone another specifically arises because device 600 is a wearable EMGdevice that advantageously accommodates the movements of a user and/ordifferent user forms. As described in more detail later on, each of podstructures 601, 602, 603, 604, 605, 606, 607, and 608 may correspond toa respective housing (e.g., housing 490 of sensor 400) of a respectivecapacitive EMG sensor adapted to, in use, resistively couple to theuser's skin in accordance with the present systems, articles, andmethods.

Device 600 includes eight pod structures 601, 602, 603, 604, 605, 606,607, and 608 that form physically coupled links thereof. Wearable EMGdevices employing pod structures (e.g., device 600) are used herein asexemplary wearable EMG device designs, while the present systems,articles, and methods may be applied to wearable EMG devices that do notemploy pod structures (or that employ any number of pod structures).Thus, throughout this specification, descriptions relating to podstructures (e.g., functions and/or components of pod structures) shouldbe interpreted as being applicable to any wearable EMG device design,even wearable EMG device designs that do not employ pod structures(except in cases where a pod structure is specifically recited in aclaim).

In exemplary device 600 of FIG. 6, each of pod structures 601, 602, 603,604, 605, 606, 607, and 608 comprises a respective housing, with eachhousing being akin to a respective one of housing 490 from sensor 400.Each housing may comprise substantially rigid material that encloses arespective inner volume. Details of the components contained within thehousings (i.e., within the inner volumes of the housings) of podstructures 601, 602, 603, 604, 605, 606, 607, and 608 are notnecessarily visible in FIG. 6 (e.g., the housings may be formed ofmaterial that is optically opaque). To facilitate descriptions ofexemplary device 600, some internal components are depicted by dashedlines in FIG. 6 to indicate that these components are contained in theinner volume(s) of housings and may not normally be actually visible inthe view depicted in FIG. 6, unless a transparent or translucentmaterial is employed to form the housings. For example, any or all ofpod structures 601, 602, 603, 604, 605, 606, 607, and/or 608 may includecircuitry (i.e., electrical and/or electronic circuitry). In FIG. 6, afirst pod structure 601 is shown containing circuitry 611 (i.e.,circuitry 611 is contained in the inner volume of the housing of podstructure 601), a second pod structure 602 is shown containing circuitry612, and a third pod structure 608 is shown containing circuitry 618.The circuitry in any or all pod structures may be communicativelycoupled to the circuitry in at least one other pod structure by at leastone communicative pathway (e.g., by at least one electrically conductivepathway and/or by at least one optical pathway). For example, FIG. 6shows a first set of communicative pathways 621 providing communicativecoupling between circuitry 618 of pod structure 608 and circuitry 611 ofpod structure 601, and a second set of communicative pathways 622providing communicative coupling between circuitry 611 of pod structure601 and circuitry 612 of pod structure 602.

Throughout this specification and the appended claims the term“communicative” as in “communicative pathway,” “communicative coupling,”and in variants such as “communicatively coupled,” is generally used torefer to any engineered arrangement for transferring and/or exchanginginformation. Exemplary communicative pathways include, but are notlimited to, electrically conductive pathways (e.g., electricallyconductive wires, electrically conductive traces), magnetic pathways(e.g., magnetic media), and/or optical pathways (e.g., optical fiber),and exemplary communicative couplings include, but are not limited to,electrical couplings, magnetic couplings, and/or optical couplings.

Each individual pod structure within a wearable EMG device may perform aparticular function, or particular functions. For example, in device600, each of pod structures 601, 602, 603, 604, 605, 606, and 607includes a respective capacitive EMG sensor 610 (akin to sensor 200 fromFIG. 2, sensor 300 from FIG. 3, and/or sensor 400 from FIG. 4; only onecalled out in FIG. 6 to reduce clutter) adapted to, in use, resistivelycouple to the user's skin in accordance with the present systems,articles, and methods. Each capacitive EMG sensor 610 is responsive tomuscle activity of the user, meaning that each capacitive EMG sensor 610included in device 600 to detect muscle activity of a user and toprovide electrical signals in response to the detected muscle activity.Thus, each of pod structures 601, 602, 603, 604, 605, 606, and 607 maybe referred to as a respective “sensor pod.” Throughout thisspecification and the appended claims, the term “sensor pod” is used todenote an individual pod structure that includes at least one sensorresponsive to (i.e., to detect and provide at least one signal inresponse to) muscle activity of a user.

Pod structure 608 of device 600 includes a processor 630 that processesthe signals provided by the capacitive EMG sensors 610 of sensor pods601, 602, 603, 604, 605, 606, and 607 in response to detected muscleactivity. Pod structure 608 may therefore be referred to as a “processorpod.” Throughout this specification and the appended claims, the term“processor pod” is used to denote an individual pod structure thatincludes at least one processor to process signals. The processor may beany type of processor, including but not limited to: a digitalmicroprocessor or microcontroller, an application-specific integratedcircuit (ASIC), a field-programmable gate array (FPGA), a digital signalprocessor (DSP), a graphics processing unit (GPU), a programmable gatearray (PGA), a programmable logic unit (PLU), or the like, that analyzesor otherwise processes the signals to determine at least one output,action, or function based on the signals. A person of skill in the artwill appreciate that implementations that employ a digital processor(e.g., a digital microprocessor or microcontroller, a DSP, etc.) mayadvantageously include a non-transitory processor-readable storagemedium or memory communicatively coupled thereto and storing data and/orprocessor-executable instructions that control the operations thereof,whereas implementations that employ an ASIC, FPGA, or analog processormay or may optionally not include a non-transitory processor-readablestorage medium, or may include on-board registers or othernon-transitory storage structures.

As used throughout this specification and the appended claims, the terms“sensor pod” and “processor pod” are not necessarily exclusive. A singlepod structure may satisfy the definitions of both a “sensor pod” and a“processor pod” and may be referred to as either type of pod structure.For greater clarity, the term “sensor pod” is used to refer to any podstructure that includes a sensor and performs at least the function(s)of a sensor pod, and the term processor pod is used to refer to any podstructure that includes a processor and performs at least thefunction(s) of a processor pod. In device 600, processor pod 608includes a capacitive EMG sensor 610 (not visible in FIG. 6) adapted to,in use, resistively couple to the user's skin in order to sense,measure, transduce or otherwise detect muscle activity of the user, soprocessor pod 608 could be referred to as a sensor pod. However, inexemplary device 600, processor pod 608 is the only pod structure thatincludes a processor 630, thus processor pod 608 is the only podstructure in exemplary device 600 that can be referred to as a processorpod. The processor 630 in processor pod 608 also processes the EMGsignals provided by the capacitive EMG sensor 610 of processor pod 608.In alternative embodiments of device 600, multiple pod structures mayinclude processors, and thus multiple pod structures may serve asprocessor pods. Similarly, some pod structures may not include sensors,and/or some sensors and/or processors may be laid out in otherconfigurations that do not involve pod structures.

In device 600, processor 630 includes and/or is communicatively coupledto a non-transitory processor-readable storage medium or memory 640.Memory 640 may store processor-executable gesture identificationinstructions that, when executed by processor 630, cause processor 630to process the EMG signals from capacitive EMG sensors 610 and identifya gesture to which the EMG signals correspond. For communicating with aseparate electronic device (not shown), wearable EMG device 600 includesat least one communication terminal. Throughout this specification andthe appended claims, the term “communication terminal” is generally usedto refer to any physical structure that provides a telecommunicationslink through which a data signal may enter and/or leave a device. Acommunication terminal represents the end (or “terminus”) ofcommunicative signal transfer within a device and the beginning ofcommunicative signal transfer to/from an external device (or externaldevices). As examples, device 600 includes a first communicationterminal 651 and a second communication terminal 652. Firstcommunication terminal 651 includes a wireless transmitter (i.e., awireless communication terminal) and second communication terminal 652includes a tethered connector port 652. Wireless transmitter 651 mayinclude, for example, a Bluetooth® transmitter (or similar) andconnector port 652 may include a Universal Serial Bus port, amini-Universal Serial Bus port, a micro-Universal Serial Bus port, a SMAport, a THUNDERBOLT® port, or the like.

For some applications, device 600 may also include at least one inertialsensor 660 (e.g., an inertial measurement unit, or “IMU,” that includesat least one accelerometer and/or at least one gyroscope) responsive to(i.e., to detect, sense, or measure and provide at least one signal inresponse to detecting, sensing, or measuring) motion effected by a user.Signals provided by inertial sensor 660 may be combined or otherwiseprocessed in conjunction with signals provided by capacitive EMG sensors610.

As previously described, each of pod structures 601, 602, 603, 604, 605,606, 607, and 608 may include circuitry (i.e., electrical and/orelectronic circuitry). FIG. 6 depicts circuitry 611 inside the innervolume of sensor pod 601, circuitry 612 inside the inner volume ofsensor pod 602, and circuitry 618 inside the inner volume of processorpod 618. The circuitry in any or all of pod structures 601, 602, 603,604, 605, 606, 607 and 608 (including circuitries 611, 612, and 618) mayinclude any or all of: an amplification circuit to amplify electricalsignals provided by at least one EMG sensor 610, a filtering circuit toremove unwanted signal frequencies from the signals provided by at leastone EMG sensor 610, and/or an analog-to-digital conversion circuit toconvert analog signals into digital signals. The circuitry in any or allof pod structures 601, 602, 603, 604, 605, 606, 607, and 608 may includeone or more discrete component capacitor(s), resistor(s), and/oramplifier(s) in the configuration(s) previously described for sensors200, 300, and/or 400. Device 600 may also include at least one battery(not shown in FIG. 6) to provide a portable power source for device 600.

Each of EMG sensors 610 includes a respective capacitive EMG sensorresponsive to muscle activity corresponding to a gesture performed bythe user, wherein in response to muscle activity corresponding to agesture performed by the user each of EMG sensors 610 provides signals.EMG sensors 610 are capacitive EMG sensors that are adapted to, in use,resistively couple to the user's skin per the present systems, articles,and methods, as described for sensor 200 from FIG. 2, sensor 300 fromFIG. 3, or sensor 400 from FIG. 4. In particular, each EMG sensor 610includes a respective first resistive sensor electrode 671 (only onecalled out to reduce clutter) that is communicatively coupled to anamplifier (not visible in FIG. 6, but similar to amplifier 250 of sensor200) through a discrete component capacitor (not visible in FIG. 6, butakin to first capacitor 221 a of sensor 200) and a discrete componentresistor (also not visible in FIG. 6, but akin to first resistor 231 aof sensor 200), a second resistive sensor electrode 672 (only one calledout to reduce clutter) that is also communicatively coupled to theamplifier through a discrete component capacitor (not visible in FIG. 6,but akin to third capacitor 221 b of sensor 200) and a discretecomponent resistor (also not visible in FIG. 6, but akin to thirdresistor 231 b of sensor 200), and a ground electrode 673 (only onecalled out to reduce clutter). Each of the electrodes 671, 672, and 673of each EMG sensor 610 may be carried by a respective substrate, and therespective circuitry (e.g., 611, 612, and 618) of each pod structure601, 602, 603, 604, 605, 606, 607, and 608 may be carried by the samesubstrate and include the communicative pathway, amplifier, capacitor,and resistor elements previously described for sensors 200, 300, and400. For example, each respective EMG sensor 610 of each pod structure601, 602, 603, 604, 605, 606, 607, and 608 may include a respectivesubstrate, with the first and second sensor electrodes 671, 672 and theground electrode 673 of each pod structure 601, 602, 603, 604, 605, 606,607, and 608 carried by a first surface of the substrate and circuitry611, 612, 618 carried by a second surface of the substrate, the secondsurface being opposite the first surface across a thickness of thesubstrate. For each sensor 610, the circuitry respectively includes atleast an amplifier (e.g., 250, 350, 450), a first electricallyconductive pathway (e.g., 211 a, 311 a, 411 a) that communicativelycouples the first sensor electrode 671 and the amplifier, a firstcapacitor (e.g., 221 a, 321 a, 421 a) electrically coupled in seriesbetween the first sensor electrode 671 and the amplifier in the firstelectrically conductive pathway, and a first resistor (e.g., 231 a, 331a, 431 a) electrically coupled in series between the first sensorelectrode and the amplifier in the first electrically conductivepathway.

The capacitive EMG sensors 610 of wearable EMG device 600 aredifferential sensors that each implement two respective sensorelectrodes 671, 672 and a respective ground electrode 673, though theteachings herein may similarly be applied to wearable EMG devices thatemploy single-ended capacitive EMG sensors that each implement arespective single sensor electrode and/or capacitive EMG sensors thatshare a common ground electrode.

Signals that are provided by capacitive EMG sensors 610 in device 600are routed to processor pod 608 for processing by processor 630. To thisend, device 600 employs a set of communicative pathways (e.g., 621 and622) to route the signals that are output by sensor pods 601, 602, 603,604, 605, 606, and 607 to processor pod 608. Each respective podstructure 601, 602, 603, 604, 605, 606, 607, and 608 in device 600 iscommunicatively coupled to, over, or through at least one of the twoother pod structures between which the respective pod structure ispositioned by at least one respective communicative pathway from the setof communicative pathways. Each communicative pathway (e.g., 621 and622) may be realized in any communicative form, including but notlimited to: electrically conductive wires or cables, ribbon cables,fiber-optic cables, optical/photonic waveguides, electrically conductivetraces carried by a rigid printed circuit board, electrically conductivetraces carried by a flexible printed circuit board, and/or electricallyconductive traces carried by a stretchable printed circuit board.

Device 600 from FIG. 6 represents an example of a wearable EMG devicethat incorporates the teachings of the present systems, articles, andmethods, though the teachings of the present systems, articles, andmethods may be applicable to any wearable EMG device that includes atleast one EMG sensor.

Throughout this specification and the appended claims, infinitive verbforms are often used. Examples include, without limitation: “to detect,”“to provide,” “to transmit,” “to communicate,” “to process,” “to route,”and the like.

Unless the specific context requires otherwise, such infinitive verbforms are used in an open, inclusive sense, that is as “to, at least,detect,” to, at least, provide,” “to, at least, transmit,” and so on.

The above description of illustrated embodiments, including what isdescribed in the Abstract, is not intended to be exhaustive or to limitthe embodiments to the precise forms disclosed. Although specificembodiments of and examples are described herein for illustrativepurposes, various equivalent modifications can be made without departingfrom the spirit and scope of the disclosure, as will be recognized bythose skilled in the relevant art. The teachings provided herein of thevarious embodiments can be applied to other portable and/or wearableelectronic devices, not necessarily the exemplary wearable electronicdevices generally described above.

In the context of this disclosure, a memory is a processor-readablemedium that is an electronic, magnetic, optical, or other physicaldevice or means that contains or stores a computer and/or processorprogram. Logic and/or the information can be embodied in anyprocessor-readable medium for use by or in connection with aninstruction execution system, apparatus, or device, such as acomputer-based system, processor-containing system, or other system thatcan fetch the instructions from the instruction execution system,apparatus, or device and execute the instructions associated with logicand/or information.

In the context of this specification, a “non-transitoryprocessor-readable medium” can be any element that can store the programassociated with logic and/or information for use by or in connectionwith the instruction execution system, apparatus, and/or device. Theprocessor-readable medium can be, for example, but is not limited to, anelectronic, magnetic, optical, electromagnetic, infrared, orsemiconductor system, apparatus or device, provided that it is tangibleand/or non-transitory. More specific examples (a non-exhaustive list) ofthe processor-readable medium would include the following: a portablecomputer diskette (magnetic, compact flash card, secure digital, or thelike), a random access memory (RAM), a read-only memory (ROM), anerasable programmable read-only memory (EPROM, EEPROM, or Flash memory),a portable compact disc read-only memory (CDROM), digital tape, andother non-transitory media.

The various embodiments described above can be combined to providefurther embodiments. To the extent that they are not inconsistent withthe specific teachings and definitions herein, all of the U.S. patents,U.S. patent application publications, U.S. patent applications, foreignpatents, foreign patent applications and non-patent publicationsreferred to in this specification and/or listed in the Application DataSheet, including but not limited to U.S. Non-Provisional PatentApplication Ser. No. 14/553,657, U.S. Provisional Patent ApplicationSer. No. 61/909,786; U.S. Provisional Patent Application Ser. No.61/768,322 (now U.S. Non-Provisional patent application Ser. No.14/186,889); U.S. Provisional Patent Application Ser. No. 61/771,500(now U.S. Non-Provisional patent application Ser. No. 14/194,252); U.S.Provisional Patent Application Ser. No. 61/857,105 (now U.S.Non-Provisional patent application Ser. No. 14/335,668); U.S.

Provisional Patent Application Ser. No. 61/860,063 (now U.S.Non-Provisional patent application Ser. No. 14/276,575); U.S.Provisional Patent Application Ser. No. 61/866,960 (now U.S.Non-Provisional patent application Ser. No. 14/461,044); U.S.Provisional Patent Application Ser. No. 61/869,526 (now U.S.Non-Provisional patent application Ser. No. 14/465,194); U.S.Provisional Patent Application Ser. No. 61/881,064 (now U.S.Non-Provisional patent application Ser. No. 14/494,274); U.S.Provisional Patent Application Ser. No. 61/894,263 (now U.S.Non-Provisional patent application Ser. No. 14/520,081), and U.S.Provisional Patent Application Ser. No. 61/903,238 (now U.S.Non-Provisional patent application Ser. No. 14/539,773), are allincorporated herein by reference, in their entirety. Aspects of theembodiments can be modified, if necessary, to employ systems, circuitsand concepts of the various patents, applications and publications toprovide yet further embodiments.

These and other changes can be made to the embodiments in light of theabove-detailed description. In general, in the following claims, theterms used should not be construed to limit the claims to the specificembodiments disclosed in the specification and the claims, but should beconstrued to include all possible embodiments along with the full scopeof equivalents to which such claims are entitled. Accordingly, theclaims are not limited by the disclosure.

1. An electromyography (“EMG”) sensor comprising: a first sensorelectrode formed of an electrically conductive material, wherein thefirst sensor electrode comprises a first layer formed of a firstelectrically conductive material that includes copper and a second layerformed of a second electrically conductive material; an amplifier; and afirst electrically conductive pathway that communicatively couples thefirst sensor electrode and the amplifier.
 2. The EMG sensor of claim 1wherein the second electrically conductive material includes a materialselected from a group consisting of: gold, steel, stainless steel,silver, titanium, electrically conductive rubber, and electricallyconductive silicone.
 3. The EMG sensor of claim 1, further comprising: aground electrode formed of an electrically conductive material; a secondelectrically conductive pathway that communicatively couples to theground electrode; and a third electrically conductive pathway thatcommunicatively couples the first electrically conductive pathway andthe second electrically conductive pathway.
 4. The EMG sensor of claim 1wherein the EMG sensor is a differential EMG sensor that furthercomprises: a second sensor electrode formed of an electricallyconductive material, wherein the second sensor electrode comprises afirst layer formed of a first electrically conductive material thatincludes copper and a second layer formed of a second electricallyconductive material that includes a material selected from a groupconsisting of: gold, steel, stainless steel, silver, titanium,electrically conductive rubber, and electrically conductive silicone;and a second electrically conductive pathway that communicativelycouples the second sensor electrode and the amplifier.
 5. The EMG sensorof claim 1, further comprising: a first capacitor electrically coupledin series between the first sensor electrode and the amplifier in thefirst electrically conductive pathway; and a first resistor electricallycoupled in series between the first sensor electrode and the amplifierin the first electrically conductive pathway.
 6. The EMG sensor of claim1, further comprising: a housing, wherein the amplifier, the firstelectrically conductive pathway, and the first layer of the first sensorelectrode are all substantially contained within the housing, thehousing including a hole, and wherein at least a portion of the secondlayer of the first sensor electrode extends out of the housing throughthe hole.
 7. The EMG sensor of claim 1, further comprising: a substratehaving a first surface and a second surface, the second surface oppositethe first surface across a thickness of the substrate, wherein the firstsensor electrode is carried by the first surface of the substrate andthe amplifier is carried by the second surface of the substrate.
 8. TheEMG sensor of claim 7 wherein the first electrically conductive pathwayincludes at least one electrically conductive trace carried by thesecond surface of the substrate and at least one via that extendsthrough the substrate.
 9. A wearable electromyography (“EMG”) devicecomprising: at least one EMG sensor responsive to muscle activitycorresponding to a gesture performed by a user of the wearable EMGdevice, wherein in response to muscle activity corresponding to agesture performed by the user the at least one EMG sensor providessignals, and wherein the at least one EMG sensor includes: a firstsensor electrode formed of an electrically conductive material, whereinthe first sensor electrode of the at least one EMG sensor comprises afirst layer formed of a first electrically conductive material thatincludes copper and a second layer formed of a second electricallyconductive material; an amplifier; and a first electrically conductivepathway that communicatively couples the first sensor electrode and theamplifier; a processor communicatively coupled to the at least one EMGsensor to process signals provided by the at least one EMG sensor; andan output terminal communicatively coupled to the processor to transmitsignals output by the processor.
 10. The wearable EMG device of claim 9wherein the second electrically conductive material includes a materialselected from a group consisting of: gold, steel, stainless steel,silver, titanium, electrically conductive rubber, and electricallyconductive silicone.
 11. The wearable EMG device of claim 9 wherein theat least one EMG sensor further includes: a ground electrode formed ofan electrically conductive material; a second electrically conductivepathway that communicatively couples to the ground electrode; and athird electrically conductive pathway that communicatively couples thefirst electrically conductive pathway and the second electricallyconductive pathway.
 12. The wearable EMG device of claim 9 wherein theat least one EMG sensor includes at least one differential EMG sensor,and wherein the at least one differential EMG sensor further includes: asecond sensor electrode formed of an electrically conductive material,wherein the second sensor electrode of the at least one EMG sensorcomprises a first layer formed of a first electrically conductivematerial that includes copper and a second layer formed of a secondelectrically conductive material that includes a material selected froma group consisting of: gold, steel, stainless steel, silver, titanium,electrically conductive rubber, and electrically conductive silicone;and a second electrically conductive pathway that communicativelycouples the second sensor electrode and the amplifier.
 13. The wearableEMG device of claim 9 wherein the at least one EMG sensor furtherincludes: a first capacitor electrically coupled in series between thefirst sensor electrode and the amplifier in the first electricallyconductive pathway; and a first resistor electrically coupled in seriesbetween the first sensor electrode and the amplifier in the firstelectrically conductive pathway.
 14. The wearable EMG device of claim 9,further comprising: at least one housing that at least partiallycontains the at least one EMG sensor, wherein the amplifier, the firstelectrically conductive pathway, and the first layer of the first sensorelectrode are all substantially contained within the at least onehousing, the at least one housing including a hole, and wherein at leasta portion of the second layer of the first sensor electrode extends outof the at least one housing through the hole.
 15. An electromyography(“EMG”) sensor comprising: a first sensor electrode to couple to auser's skin, wherein the first sensor electrode includes a first layerof a first electrically conductive material that includes copper and asecond layer of a second electrically conductive material; and circuitrycommunicatively coupled to the first sensor electrode.
 16. The EMGsensor of claim 15 wherein the second electrically conductive materialincludes a material selected from a group consisting of: gold, steel,stainless steel, silver, titanium, electrically conductive rubber, andelectrically conductive silicone.
 17. The EMG sensor of claim 15 whereinthe circuitry includes at least a portion of at least one circuitselected from a group consisting of: an amplification circuit, afiltering circuit, and an analog-to-digital conversion circuit.
 18. TheEMG sensor of claim 17 wherein the circuitry includes: a high-passfilter that includes a first capacitor and a first resistor; and alow-pass filter that includes the first resistor and a second capacitor.19. The EMG sensor of claim 15 wherein a resistive coupling between thefirst sensor electrode and the user's skin includes an impedance, andwherein the EMG sensor further comprises: a first resistor to dominatethe impedance of the resistive coupling between the first sensorelectrode and the user's skin, wherein the first resistor iselectrically coupled in series between the first sensor electrode andthe circuitry and wherein the first resistor has a magnitude of at least1 kΩ.
 20. The EMG sensor of claim 19 wherein the first resistor has amagnitude of at least 10 kΩ.
 21. The EMG sensor of claim 15, furthercomprising: a ground electrode to couple to the user's skin, wherein theground electrode includes a plate of electrically conductive material,and wherein the ground electrode is communicatively coupled to thecircuitry.
 22. The EMG sensor of claim 15, further comprising: a firstcapacitor to galvanically isolate the circuitry from the user's skin,the first capacitor electrically coupled in series between the firstsensor electrode and the circuitry.
 23. The EMG sensor of claim 15,further comprising: a housing, wherein the circuitry and the first layerof the first sensor electrode are both substantially contained withinthe housing, the housing including a hole, and wherein at least aportion of the second layer of the first sensor electrode extends out ofthe housing through the hole.
 24. The EMG sensor of claim 15 wherein theEMG sensor is a differential EMG sensor that further comprises: a secondsensor electrode to couple to the user's skin, wherein the second sensorelectrode includes a first layer of the first electrically conductivematerial that includes copper and a second layer of the secondelectrically conductive material, wherein the second electricallyconductive material includes a material selected from a group consistingof: gold, steel, stainless steel, silver, titanium, electricallyconductive rubber, and electrically conductive silicone, and wherein thecircuitry is communicatively coupled to the second sensor electrode.